gstsegment: Handle positions before the segment properly

Fixes for gst_segment_position_from_running_time_full() when
converting running_times that precede the segment start (or
stop in a negative rate segment)

The return value was incorrectly negated in those cases.

Add some more unit test checks for those cases, and especially
for segments with offsets.

gst/gstsegment.c

@@ -992,8 +992,9 @@ gst_segment_position_from_running_time (const GstSegment * segment,
  * When 1 is returned, @running_time resulted in a positive position returned
  * in @position.
  *
- * When this function returns -1, the returned @position should be negated
- * to get the real negative segment position.
+ * When this function returns -1, the returned @position was < 0, and the value
+ * in the position variable should be negated to get the real negative segment
+ * position.
  *
  * Returns: a 1 or -1 on success, 0 on failure.
  *
@@ -1036,12 +1037,15 @@ gst_segment_position_from_running_time_full (const GstSegment * segment,
       *position = base - running_time;
       if (G_UNLIKELY (abs_rate != 1.0))
         *position = ceil (*position * abs_rate);
-      if (start + segment->offset > *position) {
-        *position -= start + segment->offset;
-        res = -1;
-      } else {
+      if (start + segment->offset >= *position) {
+        /* The TS is before the segment, but the result is >= 0 */
         *position = start + segment->offset - *position;
         res = 1;
+      } else {
+        /* The TS is before the segment, and the result is < 0
+         * so negate the return result */
+        *position = *position - (start + segment->offset);
+        res = -1;
       }
     }
   } else {
@@ -1057,15 +1061,24 @@ gst_segment_position_from_running_time_full (const GstSegment * segment,
         res = 1;
       }
     } else {
+      /* This case is tricky. Requested running time precedes the
+       * segment base, so in a reversed segment where rate < 0, that
+       * means it's before the alignment point of (stop - offset).
+       * Before = always bigger than (stop-offset), which is usually +ve,
+       * but could be -ve is offset is big enough. -ve position implies
+       * that the offset has clipped away the entire segment anyway */
       *position = base - running_time;
       if (G_UNLIKELY (abs_rate != 1.0))
         *position = ceil (*position * abs_rate);
-      if (G_UNLIKELY (stop < segment->offset - *position)) {
-        *position -= segment->offset - stop;
-        res = -1;
-      } else {
+
+      if (G_LIKELY (stop + *position >= segment->offset)) {
         *position = stop + *position - segment->offset;
         res = 1;
+      } else {
+        /* Requested position is still negative because offset is big,
+         * so negate the result */
+        *position = segment->offset - *position - stop;
+        res = -1;
       }
     }
   }

tests/check/gst/gstsegment.c

@@ -869,11 +869,105 @@ GST_START_TEST (segment_full)
   segment.offset = 0;
   gst_segment_set_running_time (&segment, GST_FORMAT_TIME, 100);
   fail_unless_equals_int (segment.base, 100);
+
   fail_unless (gst_segment_position_from_running_time_full (&segment,
-          GST_FORMAT_TIME, 70, &pos) == -1);
+          GST_FORMAT_TIME, 70, &pos) == 1);
+  fail_unless_equals_int (pos, 120);
+
   fail_unless (gst_segment_position_from_running_time_full (&segment,
           GST_FORMAT_TIME, 140, &pos) == 1);
   fail_unless_equals_int (pos, 190);
+
+  /* Test a non-1.0 rate that lands right before the segment, but still +ve */
+  segment.rate = 1.1;
+  segment.start = 100;
+  segment.offset = 0;
+  segment.stop = 500;
+  segment.position = 40;
+  segment.base = 150;
+  segment.time = 10000;
+  fail_unless (gst_segment_position_from_running_time_full (&segment,
+          GST_FORMAT_TIME, 140, &pos) == 1);
+  fail_unless (pos == 89);
+  /* And now one that should give a position < 0 */
+  fail_unless (gst_segment_position_from_running_time_full (&segment,
+          GST_FORMAT_TIME, 0, &pos) == -1);
+  fail_unless (pos == 65);
+
+  /* Test a non-1.0 negative rate that lands right after the (reversed) segment, but still +ve position */
+  segment.rate = -2.0;
+  segment.start = 100;
+  segment.offset = 0;
+  segment.stop = 500;
+  segment.position = 150;
+  segment.base = 133;
+  segment.time = 10000;
+  fail_unless (gst_segment_position_from_running_time_full (&segment,
+          GST_FORMAT_TIME, 200 + 133 + 20, &pos) == 1);
+  fail_unless (pos == 60);
+  /* And now one that should give a position < 0, reported as a negated value */
+  fail_unless (gst_segment_position_from_running_time_full (&segment,
+          GST_FORMAT_TIME, 200 + 133 + 70, &pos) == -1);
+  fail_unless (pos == 40);
+
+  /* Test gst_segment_position_from_running_time_full() with offsets */
+  segment.rate = 2.0;
+  segment.start = 100;
+  segment.offset = 100;
+  segment.stop = 500;
+  segment.position = 150;
+  segment.base = 175;
+  segment.time = 10000;
+  /* Position before the segment but >= 0 */
+  fail_unless (gst_segment_position_from_running_time_full (&segment,
+          GST_FORMAT_TIME, 75, &pos) == 1);
+  fail_unless (pos == 0);
+  fail_unless (gst_segment_position_from_running_time (&segment,
+          GST_FORMAT_TIME, 75) == -1);
+
+  /* Position before the segment and < 0 */
+  fail_unless (gst_segment_position_from_running_time_full (&segment,
+          GST_FORMAT_TIME, 65, &pos) == -1);
+  fail_unless (pos == 20);      /* Actually -20 */
+  fail_unless (gst_segment_position_from_running_time (&segment,
+          GST_FORMAT_TIME, 65) == -1);
+
+  /* After the segment */
+  fail_unless (gst_segment_position_from_running_time_full (&segment,
+          GST_FORMAT_TIME, 175 + 150 + 10, &pos) == 1);
+  fail_unless (pos == 520);
+  fail_unless (gst_segment_position_from_running_time (&segment,
+          GST_FORMAT_TIME, 175 + 150 + 10) == -1);
+
+  /* And with negative rate, so the segment is reversed */
+  segment.rate = -2.0;
+
+  /* Before the segment */
+  fail_unless (gst_segment_position_from_running_time_full (&segment,
+          GST_FORMAT_TIME, 75, &pos) == 1);
+  fail_unless (pos == 600);
+  fail_unless (gst_segment_position_from_running_time (&segment,
+          GST_FORMAT_TIME, 75) == -1);
+
+  /* Position after the segment and < 0 */
+  fail_unless (gst_segment_position_from_running_time_full (&segment,
+          GST_FORMAT_TIME, 400, &pos) == -1);
+  fail_unless (pos == 50);      /* Actually -50 */
+  fail_unless (gst_segment_position_from_running_time (&segment,
+          GST_FORMAT_TIME, 400) == -1);
+
+  /* Position after the segment and >= 0 */
+  fail_unless (gst_segment_position_from_running_time_full (&segment,
+          GST_FORMAT_TIME, 325 + 10, &pos) == 1);
+  fail_unless (pos == 80);
+  fail_unless (gst_segment_position_from_running_time (&segment,
+          GST_FORMAT_TIME, 325 + 10) == -1);
+
+  /* Big offset can clip away an entire reversed segment and produce a negative position anyway */
+  segment.offset = 1000;
+  fail_unless (gst_segment_position_from_running_time_full (&segment,
+          GST_FORMAT_TIME, 75, &pos) == -1);
+  fail_unless (pos == 300);     /* Actually -300 */
 }
 
 GST_END_TEST;